A radio wave propagation characteristic estimation system (radio wave propagation simulator) is used to support the disposition of the base stations and parent machines in a wireless communication system. Using this radio wave simulator, received power at an arbitrary receiving point and delay spread are evaluated and suitable installation places of transmission stations are determined. As a result, efficiency improvement, such as reduction in the number of base stations to be disposed, is achieved.
Radio wave propagation simulations are broadly classified into those using a statistical technique and those using a decision theoretical technique. In the statistical technique, an estimation expression for propagation loss having the distance and frequency as arguments is given. Parameters are determined by the multivariate analysis on the basis of a large number of data obtained by actual measurements of the propagation loss. In general, propagation of radio waves is varied from section to section by reflection or transmission caused by structures or indoor objects. According to the statistical technique, the median of section variation is given.
On the other hand, the decision theoretical technique is a technique of regarding radio waves emitted from an antenna is regarded as a collection of a large number of radio wave rays, supposing each ray to be repeated in reflection and transmission and propagated, and combining rays arriving at an observation point to find the propagation loss and the delay quantity. The present technique is called ray tracing method. In the ray tracing method, influences of reflection, transmission and diffraction caused by actual structures are taken into consideration, and consequently the section variation itself at the observation point can be known.
The ray tracing methods are further broadly divided into the ray launching method and the imaging method. The ray launching technique is a technique of emitting rays discretely at constant angle intervals, successively tracing their trajectories, and regarding rays passing through near the receiving point as rays that have arrived at the receiving point.
On the other hand, the imaging method is a technique of determining reflection and transmission paths of rays coupling the transmitting point and the receiving point to each other by finding a mirror reflection point for the reflecting surface. If the transmitting and receiving points and the reflecting and transmitting objects are specified, the reflection and transmission paths are uniquely found. In the imaging method, therefore, strict ray propagation paths can be searched for. Details of the ray launching method and the imaging method are disclosed in, for example, Patent reference 1.
Patent Reference 1: JP, H9-33584, A